The objective of this research project is to assess the factors responsible for differences in the substrate specificities among cytochrome P-450-dependent microsomal mixed-function oxidase systems (MFO) from various sources. Present work involved the purification of cytochrome P-450, cytochrome b5, NADPH-cytochrome P-450 reductase and NADH-cytochrome c reductase from rabbit pulmonary and hepatic microsomal fractions. Components of the MFO are being examined by UV-vis spectroscopy, electron paramagnetic resonance spectroscopy, SDS-gel electrophoresis, and by their activities in reconstituted systems. Structural and immunochemical properties of the enzymes are also being investigated. The long-range objectives of this work are to determine the influence of: 1) multiple forms of the enzymic components of the MFO systems, 2) endogenous compounds, and 3) exogenous compounds (substrates, inducers and inhibitors) on the substrate specificities of MFO systems from different tissues and species.